1. Field of the Invention
The present invention relates to a data sensing timing modulating circuit, particularly for non-volatile memories.
2. Discussion of the Related Art
It is known that in memories which use dynamic sense amplifiers, and similarly with static amplifiers, i.e., amplifiers that do not read the data of the memory at particular times and therefore allow reading at any freely selectable time, it is very important to determine the moment of data sensing and the sensitivity of the amplifier, i.e., the timing of the control step meant to capture the data, so as to obtain the best possible result in any operating condition.
The sensing step generally follows a first precharge step that very quickly brings the bit lines to which the various memory cells are connected to the operating level and equalizes them. Indeed, because they are equalized, these lines must then have time enough to assume a difference, however small, allowing certain and correct data reading.
The time intervals that determine a timing for reading a non-volatile memory are not absolute but depend on a certain number of variables, such as:
the conductivity characteristics of the memory cells; PA1 the levels transmitted to the cells at the given instant; PA1 the capacitance of the associated lines; PA1 the minimum sensitivity of the sense amplifiers; PA1 the impedances of the memory access paths; PA1 the presence/absence of supply voltage boosting circuits; and PA1 the operating temperature.
It is thus evident that it is not possible to establish beforehand a given data sensing timing, with the purpose of optimizing the read times of a memory device. Even if one considerably expands the timing of the sensing step, with a consequent slowing of the data capture, the case may in fact occur in which the levels transmitted to the cells are still insufficient to determine their possible conductivity, and if one proceeded with the reading operation, the result would be unreliable. A memory device with scarcely conductive cells requires a longer settling time than a similar device with more conductive cells.
In any case, the sensing step must be followed by a data capture step that must be performed as quickly as possible. European patent application no. 95830336.4 filed on Jul. 28, 1995 in the name of the same Applicant disclosed a circuit for generating a signal with a slope capable of being modulated, which is a function of the conductivity of a memory cell. Slope modulation is therefore performed in close correlation with the conductivity of the memory cell. This application is incorporated herein by reference.
One object of the present invention is therefore to provide a data sensing timing modulating circuit, particularly for non-volatile memories, that is capable of modulating the data sensing and capture times as a function of the conductivity of the memory cells.
Another object of the present invention is to provide a data sensing timing modulating circuit, particularly for non-volatile memories, that is capable of correlating the moment when the data sensing step starts to the conductivity of the memory cells.
Another object of the present invention is to provide a data sensing timing modulating circuit, particularly for non-volatile memories, that allows optimization of the sensitivity of the sense amplifiers of the memory device, as a function of the conductivity of the memory cells of said device.
Another object of the present invention is to provide a data sensing timing modulating circuit for a memory device that allows suspension and delay of the timing of the extraction of the data item if the minimal conditions for correct and certain reading are not achieved.
Another object of the present invention is to provide a data sensing timing modulating circuit for a memory device, which allows modulation of the data sensing timing according to the voltage applied to the memory device at a given instant.
Another object of the present invention is to provide a data sensing timing modulating circuit that allows modulation of the timing of the data according to the operating temperature of the memory device at a given instant.
Another object of the present invention is to provide a data sensing timing modulating circuit that allows modulation of data timing according to the intrinsic conductivity characteristics of the memory device.
Another object of the present invention is to provide a data sensing timing modulating circuit that allows modulation of the data timing according to the technological and process characteristics used in the memory device.
Another object of the present invention is to provide a sensing timing modulating circuit for the data of a memory device that is highly reliable and relatively easy to produce at competitive costs.